1. Field of the Invention
The present invention relates to a light reflection type fingerprint sensor, and more particularly, to a fingerprint sensor which improves the light efficiency of an optical-TFT (thin film transistor) in a unit cell by using a microlens.
2. Description of the Related Art
As information communication devices become smaller, cheaper, and modularized, personal information security devices through obtainment of bioinformation of an individual are gradually made small and thin. A typical bioinformation is a fingerprint. A method of recognizing a physical system that is conventional security device has been replaced by bioinformation obtainment method. There are various methods of obtaining the bioinformation and a typical device therefor is a fingerprint sensor. The fingerprint sensor that is presently used includes an optical type using an image sensor and a prism and an electrostatic type using the difference in thickness of a pattern of a fingerprint structure.
FIG. 1 is a cross-sectional view of a unit cell of a light reflection type fingerprint sensor that is an example of a conventional fingerprint sensor. Referring to FIG. 1, the unit cell of the fingerprint sensor includes a light emitting portion 10, a transparent substrate 20, an optical-TFT 30, and an electric-TFT 40. TFTs 30 and 40 are manufactured on the transparent substrate 20 that is a glass substrate. A backlight of a liquid crystal display device can be used as the light emitting portion 10.
An input light 12 emitted by the light emitting portion 10 and transmitting the TFTs 30 and 40 is reflected by a fingerprint structure 50. The reflected light is converted to an electric signal by the optical-TFT 30 formed on the substrate 20 and stored as electric charges. The stored electric charges are converted to an electric signal by the electric-TFT 40. When the electric signal is measured and processed in an appropriate method, the fingerprint structure 50 by the optical reflection can be checked.
In the optical reflection type fingerprint sensor of FIG. 1, there is a limit in reducing the size of a light source and an accurate image cannot be obtained because information is obtained from a reflected image. Also, in a fingerprint sensor using a contact light emitting device that is another type of the fingerprint sensor, since light is dispersed at a boundary surface between a light receiving device and a transparent insulation adhesive, adjacent pixel is affected.